A federal judge on Tuesday refused to toss out claims by thousands of emergency workers who sued New York City and about 150 private contractors after the workers were sickened by dust at the World Trade Center site.

Judge Alvin K. Hellerstein dismissed claims against Consolidated Edison Co. and companies controlled by developer Larry Silverstein, saying they did not have legal control over the area and therefore were not liable for damages.

But Hellerstein said the city, its contractors, and the Port Authority of New York and New Jersey were only partially immune from lawsuits, with the precise scope and extent of the immunity varying according to date, place and activity.

Andrew J. Carboy, a lawyer for plaintiffs, called the judge's decision "a first step forward in the legal system for these other victims of 9-11."

Carboy, who represents 210 clients, mostly firefighters, said Hellerstein's decision comes as the number of people making claims climbs as high as 8,000.

Michael A. Cardozo, the city's top lawyer, said a close study of the facts surrounding the claims will show that the city and its contractors were not liable.

Hellerstein said he will appoint a special master to help eliminate claims that should not be pressed and oversee a case that is "likely to become unmanageable."

"If even a minority of the plaintiffs suffered serious injuries to their respiratory tracts arising from the acrid air of September 11, their claims deserve to be heard when a recovery could make a difference in their lives," the judge wrote.

He said the defendants also are entitled to swift resolution. "The scar to the public interest needs to be cleansed, speedily, in good time," he said.

The workers claim the city and contractors were negligent in monitoring the air and assuring the safety of crews who cleaned up the World Trade Center site for months after the Sept. 11, 2001 terrorist attacks.

The judge noted that a study released in September showed that approximately 70 percent of the 10,000 workers who were tested reported that they suffer from new or substantially increased respiratory problems since 9/11.

"The workers at the site were presented with a dangerous environment, below and surrounding their work activities, threatening their health and safety," the judge said.